This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled Electrodes Of Electron Gun earlier filed in the Korean Industrial Property Office on Nov. 19, 1999, and there duly assigned Serial No. 99-51493 by that Office.
1. Field of the Invention
The present invention relates to a cathode ray tube (CRT), and more particularly, to electrodes for forming an electron lens having a large diameter, and an electron gun for a CRT using the electrodes.
2. Description of the Related Art
In general, a CRT has a panel, or screen, where a fluorescent film is formed, and a funnel coupled to the panel forming a seal. An electron gun is sealed inside a neck portion of the funnel, and a deflection yoke is installed at a cone portion. Examples of such electron guns are found in the following patents incorporated by reference herein: U.S. Pat. No. 4,766,344 to Donald L. Say entitled In-Line Electron Gun Structure For Color Cathode Ray tube Having Oblong Apertures; U.S. Pat. No. 6,013,976 to Richard M. Gorsky et al. entitled In-Line SB Electron Gun With Large And Deep Main Lens Apertures; U.S. Pat. No. 6,081,068 to Akihito Sudo et al. entitled Color Cathode Ray Tube Having Improved Main Lens Electrodes; and U.S. Pat. No. 6,133,684 to Takahiro Kawaharada entitled Electron Gun With Polygonal Shaped Rim Electrode.
A shadow mask frame assembly having a color selection function is installed inside the panel such that an electron beam emitted from the electron gun accurately lands on the fluorescent film. Inner and outer conductive films are formed at the inner and outer circumferential surfaces of the funnel, respectively.
In the CRT having the above structure, the electron beam emitted from the electron gun is selectively deflected by the deflection yoke, and lands on the fluorescent film after passing through electron beam apertures having a color selection function, so that an image is formed.
In the CRT operating as above, a focus feature of having the electron beam emitted from the electron gun installed at the neck portion accurately land on the fluorescent film, and the size of a spot of the electron beam landing on the fluorescent film, are greatly affected by a lens formed by the electrode of the electron gun, particularly by a main lens. Thus, to obtain a superior focus feature, the diameter of the main lens should be as great as possible.
In an in-line type electron gun, three electron beam apertures are formed to have an in-line shape at at least two electrodes forming an electron lens, and the diameter of the neck portion of the funnel where the electron gun is installed is limited. Thus, making the diameter of each of the electron beam apertures greater than the distance between the centers of the two electron beam apertures adjacent to each other, is not possible.
To solve the above problem, an electron beam aperture having a large diameter, through which three electron beams passes in common, is contemplated, an example of which is shown in FIG. 1.
As shown in FIG. 1, the electrode of the electron gun forming an electron lens includes focusing electrodes 10 and 20 having outer electrode members 13 and 23 and inner electrode members 14 and 24. Here, a large diameter electron beam apertures 11 and 21 through which three electron beams pass are formed at the outer electrode members 13 and 23. Burring portions 12 and 22 are formed along the edge of the large diameter electron beam apertures 11 and 21. Also, the inner electrode members 14 and 24 are installed at the inner surfaces of the outer electrode members 13 and 23, respectively. A pair of three electron beam apertures 14R, 14G and 14B, and 24R, 24G and 24B, each being circular, having a small diameter and arranged in an in-line format, are formed at the inner electrode members 14 and 24, respectively.
In the electron gun having the above exemplary structure, when different voltages are applied to the electrodes, lines of electric force are formed between the electrodes and equipotential lines are formed in a normal direction with respect to the lines of electric force so that an electron lens is formed. The burring portions 12 and 22 formed at the edge of the large diameter electron beam apertures 11 and 21 of the electron lens, respectively, decrease the effective areas of the large diameter electron beam apertures 11 and 21. Thus, there is a limit in decreasing spherical aberration of the electron lens formed by the large diametric electron beam apertures 11 and 21. Further, the beam spot size of the electron beam passing through the large diametric electron beam apertures 11 and 21 increases undesirably. Also, the widths of the edges of the large diametric electron beam apertures 11 and 21 are relatively large due to the burring portions 12 and 22 extending from the edges of the large diametric electron beam apertures 11 and 21 toward the inner side of each of the outer electrode members 13 and 23. Since the electrical field concentrates on the end portions of the burring portions 12 and 22, designing OCV (Outer Beam Convergence Variance) that is the distance between the electron beams to excite a red fluorescent substance and a blue fluorescent substance is difficult. Here, the OCV means the eccentric distance between the electron beams landing on the red fluorescent substance and the blue fluorescent substance. That is, the OCV design of the electron beam is affected by the difference in horizontal length of the large diameter electron beam apertures 11 and 21 and the length of a bulb, and design and process error control thereof are not easy. Also, removal of the burring portions 12 and 22 of large diameter electron beam apertures 11 and 21 formed in outer electrodes 13 and 23 result in leakage current being generated by acute portions formed at the edge of the large diameter electron beam apertures, so that the electron lens is distorted.
To solve the above problems, it is an objective of the present invention to provide electrodes of an electron gun for a color CRT which can make a large diameter electron lens, minimize the spot size of the electron beam passing the large diameter electron lens, and reduce the generation of leakage current, so that distortion of the electron lens is prevented.
Accordingly, to achieve the above objective, there is provided electrodes of an electron gun including a pair of first and second outer rim electrode members installed to face one another and where large diameter electron beam apertures through which three electron beams pass are respectively formed, and first and second inner electrode member installed in the outer rim electrode members, respectively, and where three small diameter electron beam apertures are formed to have an in-line shape, wherein a burring portion is formed at the edge of the large diameter electron beam aperture of the first outer rim electrode member at one side of the outer rim electrode members facing each other, and the vertical diameter of the electron beam aperture formed in the middle of the small diameter electron beam apertures formed at the first inner electrode is formed to be greater than those of the two other small diameter electron beam apertures.
It is preferable in the present invention that the burring portion is formed at the electrode located adjacent to a cathode when it is installed at the electron gun.